Mobile electronic devices, such as smart phones, portable navigation devices and integrated navigation systems, that include GNSS (Global Navigation Satellite Systems) signal reception and processing functionality are well known and are widely employed as in-car or other vehicle navigation systems. In general terms, a known electronic device having navigation functionality comprises a processor, memory (at least one of volatile and non-volatile, and commonly both), and digital map data stored within said memory. The processor and memory cooperate to provide an execution environment in which a software operating system may be established, and additionally it is commonplace for one or more additional software programs to be provided to enable the functionality of the mobile device/PND to be controlled, and to provide various other functions.
Such devices also include a GNSS antenna, such as a GPS antenna, by means of which satellite-broadcast signals, including location data, can be received and subsequently processed to determine a current location of the device relevant to the digital map. The device may also include electronic gyroscopes and accelerometers which produce signals that can be processed to determine the current angular and linear acceleration. The determined acceleration may then be used in conjunction with location information derived from the GPS signal to determine the velocity and relative displacement of the device and thus vehicle in which it is typically mounted. Such sensors are most commonly provided in in-vehicle navigation systems, but may also be provided in the mobile device/PND itself.
In recent years, such devices have also been used in systems to alert drivers when they are approaching known locations of points of interest (POIs), which could be: speed enforcement devices (i.e. speed traps and enforcement cameras); road hazards, such as school zones, accident black spots, road works; and weather hazards such as black ice, snow, flooding and heavy rain, brush fires etc. Speed cameras are provided to slow traffic often at locations known to represent accident black spots, and may themselves represent hazards as other road users may brake suddenly and unexpectedly, which is a common response by some drivers when they see a speed enforcement device. Devices that warn a driver of the presence of a speed enforcement device improve the driver's safety since they warn the driver of the location of such hazards.
In such systems, a device having a GPS antenna and access to a database containing the location of points of interest (POIs) is typically provided in a vehicle. The device is configured to warn a driver when the vehicle, using the location information derived from the GPS signal, is approaching the location of a POI stored in the database.
In some systems, such as when the device is a navigation device and comprises a digital map representative of a navigable network, e.g. the road network, information about POIs, including their location, is typically contained in the digital map. The digital map (or mathematical graph, as it is sometimes known), in its simplest form, is effectively a database containing data representative of nodes, most commonly representative of road intersections, and lines between those nodes representing the roads between those intersections. In more detailed digital maps, lines may be divided into segments defined by a start node and end node. These nodes may be “real” in that they represent a road intersection at which a minimum of 3 lines or segments intersect, or they may be “artificial” in that they are provided as anchors for segments not being defined at one or both ends by a real node to provide, among other things, shape information for a particular stretch of road or a means of identifying the position along a road at which some characteristic of that road changes, e.g. a speed limit. The location of POIs is typically provided with reference to the segments of the digital map, although the digital map will often also contain the geographic coordinates of the POI, e.g. longitude and latitude. Accordingly, when the current location of a device is matched to the digital map, then a warning or other information about a POI can be provided when the current location of the device is moving along a segment to which the POI is associated. This allows warnings or other information to be provided only if required, however it often requires significant storage space on the device for the digital map data.
It is also known in other system to provide alerts and other information about POIs without the use of a digital map. In such systems, the locations of the POIs are stored as geographic coordinates, e.g. longitude and latitude, in a data repository often stored locally on a mobile device, but which may be periodically updated by, for example, the mobile device receiving an update by wireless communication from a central server. In these systems, a search region, commonly in the form of a cone, is defined in front of the device, and warnings and other information is provided to a user in relation to any POIs that fall within this search region. While this significantly reduces the storage space required on the device, it can lead to a number of unnecessary warnings and alerts being provided to the user. This is exemplified in FIGS. 1A, 1B and 1C. FIG. 1A illustrates an example of a false negative, i.e. no or late warning, due to a curvy road. In this example, the device is coming from the top left, and the cone, i.e. search region, will miss the POI (in this case a speed camera) due to the bend in the road. FIGS. 1B and 1C illustrate examples of a false positive, i.e. a warning for POIs that are irrelevant or will not be passed; commonly found when roads are parallel.
It is an object of embodiments of the invention to at least mitigate one or more of the problems of the prior art.